Ligaments are tough bands of tissue which serve to connect the articular extremities of bones, or to support and/or retain organs in place within the body. Ligaments are typically composed of coarse bundles of dense white fibrous tissue which are disposed in a parallel or closely interlaced manner, with the fibrous tissue being pliant and flexible but not significantly extensible.
In many cases, ligaments are torn or ruptured as a result of accidents. Various procedures have been developed to repair or replace such damaged ligaments.
For example, in the human knee, the anterior and posterior cruciate ligaments (i.e., the “ACL” and “PCL”) extend between the top end of the tibia and the bottom end of the femur. The ACL and PCL cooperate, together with other ligaments and soft tissue, to provide both static and dynamic stability to the knee. Often, the anterior cruciate ligament (i.e., the ACL) is ruptured or torn as a result of, for example, a sports-related injury. Consequently, various surgical procedures have been developed for reconstructing the ACL so as to restore substantially normal function to the knee.
In many instances, the ACL may be reconstructed by replacing the ruptured ACL with a graft ligament. More particularly, in such procedures, bone tunnels are generally formed in the top end of the tibia and the bottom end of the femur, with one end of the graft ligament being positioned in the femoral tunnel and the other end of the graft ligament being positioned in the tibial tunnel. The two ends of the graft ligament are anchored in place in various ways well known in the art so that the graft ligament extends between the bottom end of the femur and the top end of the tibia in substantially the same way, and with substantially the same function, as the original ACL. This graft ligament then cooperates with the surrounding anatomical structures so as to restore substantially normal function to the knee.
In some circumstances, the graft ligament may be a ligament or tendon which is harvested from elsewhere in the patient; in other circumstances, the graft ligament may be a synthetic device. For the purposes of the present invention, all of the foregoing are collectively referred to as a “graft ligament”.
It has been found that in securing graft tendons to tibias, because of the surface configuration of the tibia bone it often is necessary to advance a fixation screw well into a bone tunnel in the tibia, often so far that for one side of the screw to be substantially flush with the bone tunnel opening, the other side of the screw will have advanced past the outer dense hard cortical bone and entered the inner and softer cancellous bone.
It has further been found that to refrain from advancing the fixation screw to the aforementioned location (that is, to leave a portion of the screw in cortical bone all around the screw) requires that a proximal portion of the screw remain outside the bone tunnel and project from the tibia.
Thus, there is a need for a fixation screw, graft ligament anchor assembly and method which affords full advancement of a fixation screw, but at the same time permits the screw to be engaged all around in the cortical portion of the tibia or other bone.